Novel anchoring ligands for sensitizers of dye-sensitized photovoltaic devices

ABSTRACT

The present invention relates to novel pyridine compounds that can be used as anchoring ligands in metal-based sensitizing dyes of dye sensitized solar cells (DSC S ). The dyes comprising the polypyridine compounds exhibit improved light harvesting ability and lead to increased conversion efficiencies, in particular in thin TiO 2  film devices.

TECHNICAL FIELD

The present invention relates to new compounds, to the use of these compounds as ligand in organometallic compounds, in particular dyes, to organometallic compounds and dyes comprising the compounds, to the use of the compounds and of the dyes in photoelectric conversion devices, in particular dye-sensitized photovoltaic cells and to photoelectric conversion devices comprising the novel compounds or the novel dyes.

PRIOR ART AND THE PROBLEM UNDERLYING THE INVENTION

During the past two decades, mesoscopic dye-sensitized solar cells (DSCs) have emerged as promising candidates for practical photovoltaic applications by virtue of their low manufacturing costs and good conversion efficiencies DSCs with power conversion efficiencies over 10% were initially demonstrated using cis-di(thiocyanato)-bis[2,2′-bipyridyl-4,4′-dicarboxylic acid] ruthenium(II) (N3) or its bis-tetrabutylammonium (TBA) salt counterpart N719 as sensitizers in combination with a thicker titania film (>12-15 μm) and a volatile electrolyte. In DSCs, the sensitizer is one of the critical components as it absorbs sunlight and induces the charge separation process. In order to enhance power conversion efficiencies of DSCs, it is imperative to design novel sensitizers resulting in devices with higher conversion efficiencies.

It is an objective of the present invention to provide sensitizing dyes that can be used in DSCs, which exhibit an improved light-harvesting ability.

It is another objective of the present invention to provide ways of preparing dyes for such cells, which exhibit an enhanced molar absorptivity.

Furthermore, it is an objective of the present invention to provide dyes, which exhibit a red-shifted absorption band compared to dyes of the state of the art, such as N719 and Z907.

In addition, it is an objective of the invention to prepare more economic devices requiring less raw materials.

The objectives above are addressed by the present invention and therefore form part of it.

SUMMARY OF INVENTION

The present invention provides new organometallic compounds for optoelectronic devices, electrochemical devices, photoelectric conversion devices, photovoltaic cells and solar cells. In particular, the present invention provides new sensitizing organometallic compounds that can be used for sensitizing such devices.

The novel dyes comprise a new anchoring ligand comprising an extended π-conjugated system. Substituted or unsubstituted arenes comprising heteroatoms, such as thiophene and derivatives thereof, and possibly vinylene and ethynylene moieties are inserted between bi-, ter-, or polypyridine and anchoring groups, such as carboxylic acid groups, for example.

The new compounds can be used as anchoring ligands in organometallic sensitizing dyes. Surprisingly, the anchoring ligands of the invention can improve the spectral response of corresponding sensitizing dyes. In particular, the anchoring ligands increase the molar extinction coefficient of the dyes and also improve their light-harvesting ability.

Surprisingly, the dyes comprising the new anchoring ligands of the present invention result in devices having high photovoltaic performances, in particular high conversion efficiencies. In particular, devices based on thin semiconducting photoelectrode films show increased conversion efficiencies if compared to devices comprising state of the art dyes with a comparable structure.

Accordingly, in an aspect, the present invention provides a compound formula (I) or (II) below:

wherein at least one of the substituents R₁-R₈ of the compound of formula (I) and at least one of the substituents R₉-R₁₉ of the formula (II) is a substituent of formula (1) below

wherein n is an integer of 1-5, and Z is an integer of the group of successive integers 1, . . . , n, wherein any A_(Z) represents the Z^(th) moiety of the n successive moieties A, wherein any A_(Z) may be different from any other A_(Z); wherein, if more than one of R₁-R₈ of the compound of formula (I) or more than one of substituents R₉-R₁₉ of the compound of formula (II), respectively, are a substituent of formula (1), any n of such substituent may be the same or different from the n of another such substituent of formula (1), and any A_(Z) may be different from the respective A_(Z) of another such substituent of formula (1); wherein any A_(Z) is independently selected from a C4-C30 aryl, said aryl being, besides the substituent Anc, further substituted or not further substituted, and said aryl comprising from 1-10 heteroatoms; wherein said aryl, when it comprises only 4 ring carbons (C4 aryl) comprises at least one ring heteroatom selected from O, S and Se; wherein, if n≧2, A_(Z) may also be selected from vinylene

and ethynylene

, wherein said vinylene may be substituted; with the proviso that at least one A_(Z) is an aryl as defined above; wherein Anc is an anchoring group; wherein any one of R₁-R₈ of formula (1) or any one of R₉-R₁₉ of formula (II), which is not a substituent of formula (1), is, independently from the others, selected from H, halogen or a C1-C20 hydrocarbon comprising from 0 to 20 heteroatoms.

In a second aspect, the present invention provides the use of a pyridine compound of the invention as a component, for example as an anchoring ligand, of an organometallic compound. For example, the organometallic compound is a dye and/or a sensitizing dye.

In a third aspect, the present invention provides a dye of formula (XI), (XII) or (XIII):

M L₁ L₂ L₃ L₄  (XI)

M L₅ L₃ L₄ L₆  (XII)

M L₅ L₂ L₄  (XIII)

wherein M is a metal atom selected from Ru, Os, Ir, Re, Rh, and Fe; preferably from Ru, Os, and Rh; wherein L₁ is a bipyridine ligand of formula (I), (III) or (V) as defined herein; wherein L₂ is, independently from L₁, a ligand of formula (I), (III) or (V) as defined herein or a bidentate ligand being a C3-C30 hydrocarbon comprising from 2 to 20 heteroatoms; wherein L₃, L₄ and L₆ are monovalent ligands independently selected from H₂O, —Cl, —Br, —I, —CN, —NCO, —NCS and —NCSe; L₅ is a terpyridine ligand of formula (II), (IV) or (VI) as defined herein.

In a fourth aspect, the present invention provides an optoelectronic device, an electrochemical device, a photoelectric conversion device, a solar cell, and/or photovoltaic cell comprising one or more selected from the compound, the organometallic compound, the dye, and the sensitizing dye of the present invention. Preferably, the device is a dye-sensitized solar cell (DSCs).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows Scheme 1 illustrating the synthesis of compound 2, which can be used as an anchoring ligand in accordance with the invention.

FIG. 2 shows Scheme 2 illustrating the synthesis of compounds 3 a and 3 b, which represent heteroleptic dyes according to the invention, the dyes comprising compound 2 as an anchoring ligand.

FIG. 3 shows Scheme 3 illustrating the synthesis of compound 4, which is a homoleptic dye according to the invention, the dye comprising two times compound 2 as anchoring ligands.

FIG. 4 shows examples of terpyridine compounds of the present invention.

FIG. 5 shows examples of dyes of the present invention.

FIG. 6 shows examples of bipyridine compounds of the present invention.

FIG. 7 shows the electronic absorption spectrum of compound 3 b.

FIG. 8 shows the photocurrent-voltage characteristics of dye-sensitized solar cells with compound 3 a (blue rhombi line, Example 6), compound 3 b (green triangle line, Example 7) and compound 3 a with one equivalent tetrabutylammonium hydroxide (red square line). Respective dark currents are shown with broken lines. The cells comprise a double layer (7+5 μm) TiO₂ film. Z946 (a low-volatile) electrolyte was used in these devises and the composition of the electrolyte is described in the examples. Conversion efficiencies with these dyes according to the invention were all in the range of 6.6-7.6.

FIG. 9 shows IPCE spectra obtained with the same cells as described with respect to FIG. 8.

FIG. 10 shows the photocurrent-voltage characteristics of dye-sensitized solar cells with sensitizer compound 3 b of the present invention, without coadsorbant (blue rhombi line) or coadsorbed with different coadsorbants (3 b+DINHOP in 4:1 ratio, red square line); (3 b+GBA in 1:1 ratio, green triangle line, see examples) on the TiO₂ surface. Cells comprise a double layer (8.5+5 mm) TiO₂ film. Conversion efficiencies with these dyes according to the invention were all in the range of 7.5-8 (Examples 8-10).

FIG. 11 shows IPCE spectra obtained with the same cells as described with respect to FIG. 10.

FIG. 12 shows the stability of the cells as shown in FIGS. 10 and 11 over 1000 hours under the visible light-soaking (1 sun; 100 mW/cm²) at 60° C. It can be seen that short-circuit photocurrent density (J_(sc)), open current voltage (V_(OC)), fill factor (FF) and conversion efficiency (%) do change only marginally in this time, resulting in a stability of 90-106% (Examples 15-17).

FIG. 13 shows the photocurrent-voltage characteristics of dye-sensitized solar cells with sensitizer compound 3 b of the present invention adsorbed with coadsorbant guanidine buryric acid (3 b+GBA) on a 5 μm single film TiO₂ photoelectrode (red squares line). These cells of the invention are compared to corresponding cells prepared with sensitizer Z907 [cis-RuLL′(SCN)₂] (L=4,4′-dicarboxylic acid-2,2′-bipyridine, L′=4,4′-dinonyl-2,2′-bipyridine) co-adsorbed with GBA of the state of the art (blue rhombi line) (Examples 11 and 12).

FIG. 14 shows IPCE spectra obtained with the same cells as described with respect to FIG. 13. Cells with a 5 μm single thin film TiO₂ comprising a dye according to the invention exhibit about 24% increased conversion efficiencies if compared to the same cells with a dye of the state of the art. Conversion efficiencies of 7% are obtained with dyes of the invention, which is close to the efficiencies obtained with the much thicker cells with a doubled layer TiO₂ film.

FIG. 15 shows the same as FIG. 13, with the difference that cells comprising a 3 μm single film TiO₂ photoelectrode are used (Examples 13 and 14).

FIG. 16 shows IPCE spectra obtained with the same cells as described with respect to FIG. 15. Cells comprising the dye of the invention have more than 5% higher conversion efficiencies than cells comprising structurally comparable dyes of the state of the art.

FIG. 17 shows electronic absorption and emission spectra of the compound 4 (bis (tetrabutylammonium)-cis-dithio cyanato-di [5-(4′-(5-carboxythiophen-2-yl)-2,2′-bipyridin-4-yl)thiophene-2-carboxylate]ruthenium(II)) according to the invention and of the dye N719 [bis(tetrabutylammonium)-cis-dithiocyanato-bis(4′-carboxy-2,2′-bipyridine-4-carboxylate)ruthenium(II)] of the state of the art (Example 22).

FIG. 18 shows the absorption spectra of compound 4 (upper, blue line) and N719 (lower, red line) adsorbed on 3.3 μm thin transparent mesoporous TiO₂ films.

FIG. 19 shows IPCE (Incident-Photon-to-electron Conversion Efficiency) spectra of compound 4 of the invention (blue rhombi line) and N719 (red squares line) sensitizers on 3.3 μm thin nanocrystalline TiO₂ films.

FIG. 20 shows photocurrent-voltage characteristics of dye-sensitized solar cells with compound 4 (blue rhombi line) and N719 (red square line) dyes (AM 1.5G; 100 mW cm⁻²). Cell area: 0.158 cm².

FIG. 21 Schematically illustrates the structure of an embodiment of the dye-sensitized solar cell of the present invention.

FIG. 22 Schematically shows the structure of the light absorption layer (3) of the dye-sensitized solar cell shown in FIG. 21.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The pyridine compounds of the present invention are useful as ligands in organometallic compounds, in particular of metal based sensitizing dyes. The ligands are suitable as anchoring ligands, allowing the anchoring of the entire dye to a surface of choice, for example to a semiconductor surface. The new anchoring ligands comprise an extended π-conjugated system. Substituted and/or unsubstituted arenes comprising one or more heteroatoms, such as thiophene and derivatives thereof, and possibly substituted and/or unsubstituted vinylene and ethynylene moieties, are inserted between mono- or polypyridine and anchoring groups, such as carboxylic acid groups.

The compounds of the invention are pyridine compounds and preferably polypyridine compounds. Term “polypyridine”, for the purpose of the present invention, refers to compounds comprising two or more pyridine moieties, such as bipyridine, terpyridine, for example. The term pyridine compounds, for the purpose of the present invention, encompasses mono-, bi-, and ter-pyridine compounds, including polypyridines comprising more pyridine units.

The pyridine compounds of the invention, as exemplified by formula (I) and (II), may by further substituted in addition to the presence of at least one substituent of formula (1):

In particular, substituents R₁-R₁₉, if they are not substituents of formula (1), may be selected from H, halogen or a C1-C20 hydrocarbon comprising from 0 to 20 heteroatoms.

According to a preferred embodiment, R₁-R₁₉ are selected, independently one from the others, selected from H, halogen and a C1-C15 hydrocarbon comprising from 0-15, preferably O-10 heteroatoms, preferably C1-C10 hydrocarbon comprising 0-10, preferably 0-5 heteroatoms, and more preferably C1-05 hydrocarbon comprising from 0 to 5 heteroatoms. Further embodiments and preferred embodiments of substituents R₁-R₁₉ (which are different from the substituent of formula (1)), are exactly as defined for substituents R₅₁-R₁₄₃ further below, but are, of course, independently selected from said substituents R₅₁-R₁₄₃.

According to an embodiment, one or both selected from R₃ and R₆ in the compound of formula (I) are selected from substituents of formula (1); and/or one, two or all three selected from R₁₁ and R₁₄ and R₁₇ in the compound of formula (II) are selected from substituents of formula (1).

In the compounds of formula (I) and (II) above, as well in further embodiments of these compounds described further below, said substituted or unsubstituted arene comprising one or more heteroatoms, and possibly in addition vinylene and ethynylene moieties, is generally referred to herein as A_(Z). Since n is an integer from 1-5, the invention provides the following successions of A_(Z): n=1: -A₁-; n=2: -A₁-A₂-; n=3: -A₁-A₂-A₃-; n=4: -A₁-A₂-A₃-A₄-; n=5: -A₁-A₂-A₃-A₄-A₅-. According to a preferred embodiment, n is an integer selected from 1-3, preferably 1-2. Most preferably, n is 1 or 2.

Each pyridine compound of the invention comprises at least one substituent of formula (1): If the compound comprises two or more substituents of formula (1), each such substituent may be the same or different from the other such substituents.

According to an embodiment, the compound comprises one or more, preferably exactly one, substituent of formula (1) on each pyridine ring comprised in the compound.

According to an embodiment, at two or more and/or possibly all of the substituents of formula (1) on the polypyridine compound are identical.

According to an embodiment, the polypyridine compound is symmetrical. The term “symmetrical” also applies in cases where there are two or more identical anchoring groups, which are differentially protonated or deptotonated and optionally provided in the form of salts. In other words, if the only asymmetry in an otherwise symmetrical compound is the nature of a cation or its absence on two separate anchoring group, this is not considered to affect the question whether or not a compound of the invention is symmetrical.

According to an embodiment of the pyridine compound of the invention, one or more (in case there more than one pyridine rings), two or more and/or possibly all substituents of formula (1) are attached to the carbon at position 4 of the pyridine ring comprising a substituent of formula (1).

Examples of the aryl moiety A_(Z) in the pyridine compound of the invention are the moieties of formula (2)-(29) given below. According to an embodiment, any moiety A_(Z), for example A₁ and/or A₂, as applicable, may be independently selected from these moieties (2)-(29), with the proviso that at least one moiety A_(Z) is selected from any one of moieties (2)-(24) below:

wherein A and B, if applicable, are each selected independently from S (sulfur), O (oxygen), and Se (selenium); X is selected from any one of C, Si, Ge, Sn or Pb; preferably from C and Si, most preferably it is C; substituents R₅₁-R₁₄₃, if applicable, are independently one from the others selected from H, halogen and a C1-C20 hydrocarbon comprising from 0 to 20 heteroatoms.

According to an embodiment, if A is S, B is O or Se within the same moiety. According to an embodiment A is S and B is O.

As indicated above, if n is greater than 1, A_(Z) may also be selected from phenylene, vinylene (

) and ethynylene (

), wherein said phenylene and vinylene may be further substituted, with the proviso that at least one A_(Z) is neither phenylen, vinylene nor ethynylene but is an aryl comprising at least one heteroatom in the aromatic ring (heteroaryl).

According to a preferred embodiment of the moieties (2)-(21) above, A is S and B is O.

According to a preferred embodiment of the pyridine compound of the invention any A_(Z), A₁ and A₂, as applicable, is independently selected from the moieties of formula (25)-(37) below, with the proviso that if n is 2 or greater, at least one moiety is selected from any one of moieties (25)-(37) below, and if n=1, said moiety A₁ (A_(Z=1)) is selected from any one of formula (30)-(37) below,

wherein R₅₁-R₇₅, R₁₃₂-R₁₄₃, if applicable, are, independently one from the others, defined as elsewhere in this specification.

Accordingly, in the compounds of the invention, if n is 1, A₁ is selected from moieties (2)-(24) as defined above, preferably from moieties (30)-(37), and, if n is ≧1, any A_(Z) may be selected from moieties (2)-(29), preferably from (25)-(37) with the proviso that at least one moiety A_(Z) in at least one substituent of formula (1) is selected from the moieties of formula (2)-(24), preferably from the moieties (30)-(37).

According to an embodiment, if in a substituent of formula (1) n is greater than 1, the first moiety A₁ (A_(Z=1)) is selected from the moieties of formula (2)-(24), preferably from (30)-(37), and most preferably from moieties (2)-(5), preferably (30), (31), (32) and (33).

According to an embodiment, n is 1 and in every substituent of formula (1), A₁ (A_(Z=1)) is selected from any one of (2)-(24), preferably (30)-(37), preferably it is the moiety of formula (30) or (32). Preferably, substituents R₅₁, R₅₂, R₅₅, and R₅₆ are H.

According to an embodiment, if n is 2 or greater, the moieties -A₁-A₂- are selected from the moieties of formula (38)-(49) below:

wherein substituents R₅₁-R₁₀₁, in as far as present, are defined as substituents R₅₁-R₁₄₃; A and B are as defined as above; and, Ar is selected from substituted or unsubstituted vinylene (moiety 25 and 26 above), ethynylene (moiety 27 above) and from a substituted or unsubstituted Ar-diyl devoid of any heteroatom; Preferably, Ar comprises from 6 to 25 carbon atoms; Preferably, Ar represents a substituted or unsubstituted phenylene, preferably, an 1,4-para-phenylene (moiety 28) or 1,3-meta-phenylene (moiety 29).

According to an embodiment, the compounds of formula (I) and (II), respectively, are selected from compounds of formula (III) and (IV) below:

wherein A₁ and A₂ are defined as A_(Z) above; wherein A₂ may be present (n=2) or may be absent (n=1), wherein, if A₂ is absent, the anchoring group Anc is directly connected to A₁; wherein at least one of A₁ and A₂ is a heteroaryl comprising an aromatic ring with at least one heteroatom selected from S, O and Se; wherein Anc is defined as above; R₂₀-R₃₄ are independently defined as R₁-R₁₉ above. Accordingly, substituents R₂₀-R₃₄ may or may not be substituents of formula (1) above and are most preferably H.

According to a still more preferred embodiment, the compounds of formula (I) and (II), respectively, are selected from compounds of formula (V) or (VI) below

wherein A₁ and A₂ are defined as A_(Z) above; A₂ may be present (n=2) or may be absent (n=1), wherein, if A₂ is absent, the anchoring group Anc is directly connected to A₁; wherein at least one of A₁ and A₂ is a heteroaryl comprising an aromatic ring with at least one heteroatom selected from S, O and Se; Anc is defined as above; wherein R₁, R₂, R₄, R₅, R₇-R₁₀, R₁₂, R₁₃, R₁₅, R₁₆, R₁₈ and R₁₉ are defined as R₁-R₁₉ above. Accordingly, these substituents may or may not be substituents of formula (1) above.

According to an embodiment of the compounds of formula (III)-(VI) above, A₂ is absent. According to another embodiment, A₁ and A₂ are identical in each respective compound of formula (III)-(VI). This does not mean that A₁ is identical to A₂, but it also may be the case.

As indicated above, substituents R₅₁-R₁₄₃ are selected, if applicable, independently one from the others, from H, halogen, and a C1-C20 hydrocarbon comprising from 0 to 20 heteroatoms.

According to a preferred embodiment, the hydrocarbon is a C1-C15 hydrocarbon comprising 0-15, preferably 0-10 heteroatoms; preferably a C1-C10 hydrocarbon comprising 0-10, preferably 0-5 heteroatoms; more preferably a C1-C5 hydrocarbon with 0-5 heteroatoms.

According to a preferred embodiment, R₅₁-R₁₄₃, including thus R₅₁-R₇₅, the hydrocarbon is independently selected from alkyl, alkenyl, alkynyl, and aryl, wherein said alkyl, alkenyl, alkynyl and aryl may be linear, branched or cyclic and optionally further substituted. The alkyl, alkenyl, alkynyl and aryl may comprise heteroatoms. For example, a heteroatom selected from O, S, N, may be provided within a hydrocarbon structure. Heteroatoms may also be provided in the form of a functional group. The number of carbons in said alkyl, alkenyl, alkynyl and aryl is as defined for the overall hydrocarbon above. Of course, if the hydrocarbon is alkenyl or alkynyl, it comprises at least 2 carbons, and if it is aryl at least 4 carbons (heteroaryl) or at least 6 carbons (phenyl).

According to an embodiment, a heteroatom as referred to in this specification is selected from halogen, in particular F, Cl, Br, and I; O, S, Se, N, P, As, Si, B, and from metals. More preferably, heteroatoms are selected from halogen, O, S, Se, and N and from halogen, even more preferably from O, S and N.

According to an embodiment, R₅₁-R₁₄₃ are independently selected from H, halogen, —CN and alkyl, wherein said alkyl may be linear, branched or cyclic and may be further substituted, and may comprise one or more heteroatoms, for example O, S and/or N, wherein said alkyl may be partially or totally halogenated. The number in carbons in said alkyl is preferably as defined for the overall hydrocarbon.

For example, R₅₁-R₁₄₃ may be selected from substituents of formula (47) below:

in which q is an integer from 1-7 and R₁₄₄ is selected from H and from C1-C5 alkyl.

According to another embodiment, R₅₁-R₁₄₃ are independently selected from H, halogen, anchoring groups as defined herein, —CN (cyano), and C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl and C4-C10 aryl, wherein said alkyl, alkenyl and alkynyl may be linear, branched or cyclic and wherein one or more carbons of said alkyl, alkenyl, alkynyl and aryl may be replaced by one or more selected from oxygen, sulphur and nitrogen, and wherein hydrogen atoms of said alkyl, alkenyl, alkynyl and aryl may partly or totally be substituted by halogen; wherein said aryl may be substituted by C1-C5 alkyl and C2-C5 alkenyl, and wherein said aryl, if is a C4 aryl, comprises at least one heteroatom selected from O, S and N in the ring so as to provide an aromatic ring.

According to another embodiment, R₅₁-R₁₄₃ are independently selected from H; halogen; —CN (cyano); C1-C5 alkyl; —NR₁₄₅R₁₄₆; —R₁₄₇—N—R₁₄₅R₁₄₆, wherein R₁₄₅ and R₁₄₆ are selected from H and C1-C5 alkyl and R₁₄₇ is a C1-C5 alk-diyl; C1-C5 alkoxyl; —R₁₄₇—O—R₁₄₈, wherein R₁₄₇ is as defined before and R₁₄₈ is a C1-C5 alkyl; and from thioalkyl. According to a more preferred embodiment, R₅₁-R₁₄₃ are independently selected H or halogen.

According to another embodiment, R₅₁-R₁₄₃ are independently selected from H, halogen, —CN (cyano), C1-C5 alkyl, C1-C5 alkoxyl. According to a more preferred embodiment, R₅₁-R₁₄₃ are independently selected H or halogen.

Preferably one, several or all of R₅₁-R₁₄₃, if applicable, are H.

According to an embodiment, the anchoring group (Anc) is selected from —COOH, —PO₃H₂, —PO₄H₂, —P(R₁₀₀)O₂H (phosphinic acid), —SO₃H₂, —CONHOH⁻, acetylacetonate, deprotonated forms of the aforementioned, salts of said deprotonated forms, and chelating groups with Π-conducting character wherein R₁₀₀ is a hydrocarbon comprising from 1 to 20 carbons and 0-20 heteroatoms, said hydrocarbon being covalently bound to the P atom of said phosphinic acid group by a carbon atom; and wherein R₁₀₀ may be further covalently connected to the bi- or polypyridine ligand carrying the anchoring group Anc. For example, the substituent R₁₀₀ may be covalently bound to a moiety A_(Z). Preferably R₁₀₀ is a C1-C10 with 0-10 heteroatoms, for example a C1-C6 hydrocarbon comprising 0-6 heteroatoms. R₁₀₀, may, for example, be selected from substituted or unsubstituted alkyls, alkenyls, alkynyls and aryls, wherein carbons of said alkyls, alkenyls, alkynyls and aryls may be replaced by a heteroatom selected from O, N, and S, and wherein said alkyls, alkenyls, and alkynyls may be linear, or branched and/or cyclic compounds.

An example of an anchoring group is acetylacetonate of formula (Anc1) below, wherein Anc1 is connected to the terminal moiety A_(n) carrying it by a covalent bond to one selected from carbon 1, 3 or 5, preferably carbon 3, of the compound of formula (Anc1):

As the skilled person appreciates, the keto and enol tautomeric forms of the anchoring group Anc1 coexist in solution, which are thus both encompassed by the present invention.

Salts of the deprotonated forms of the above anchoring groups may be selected from salts of organic or inorganic cations. Preferably the salt is selected from H+, Na+, K+, Li+ or an ammonium salt of the above compound. An example of a frequently used ammonium compound is tetrabutyl-ammonium.

Importantly, anchoring groups present in a single pyridine compound, for example the two anchoring groups in the bipyridine compounds of formula (III) and (VII), may be different. Furthermore, anchoring groups present in a single pyridine compound may be differently protonated, deprotonated and/or be provided in the form of organic or inorganic salts of deprotonated anchoring groups.

According to an embodiment, at least one anchoring group of a bi- or terpyridine compound is protonated, the other is deprotonated, for example provided as a negatively charged group or as a salt of a positively charged organic compound or of a metal.

According to a preferred embodiment, the anchoring groups are independently selected from carboxylic acid (—COOH), deprotonated forms thereof and salts thereof.

Examples of chelating anchoring groups with Π-conducting character are oxyme, dioxyme, hydroxyquinoline, salicylate, and α-keto-enolate groups.

According to an embodiment, a substituent of formula (1) comprises one or more, for example two anchoring groups Anc. For example, if n is 1, A₁ of an individual substituent of formula (1) may carry two anchoring groups Anc. According to another example, if n is 2, A₁ and A₂ of an individual substituent of formula (1) may each comprise an anchoring group Anc or A₂ of an individual substituent of formula (1) may comprise two anchoring groups.

The present invention thus provides dyes comprising one or more pyridine compounds of the invention, in particular for use as one or more anchoring ligands. The anchoring ligand is suitable to bind the dye to a surface of choice, for example to a semiconductor surface.

The dyes of the invention preferably have the formula (XI), (XII) or (XIII) as defined above.

According to an embodiment of the dye of the invention, ligand L₂ may be selected of a pyridine compound of formula (XV) below:

wherein the substituents R¹-R⁸ are selected, independently one from the other, from H, halogen, and C1-C20 hydrocarbons comprising from 0 to 20 heteroatoms.

According to an embodiment, one or more of R¹-R⁸ are selected, independently one from the other, from substituents of formula (51) below:

wherein m is an integer of 1-10, and X is an integer of the group of integers 1, . . . , m, wherein any B_(X) represents the X^(th) moiety of the m successive moieties B, wherein any B_(X) may be different from any other B_(X); wherein, if more than one of R¹-R⁸ of the compound of formula (XV) are a substituent of formula (51), any m of such substituent may be the same or different from another such substituent of formula (51), and any B_(X) may be different from the respective B_(X) of another such substituent of formula (51); wherein any B_(X) is independently selected from a C4-C20 aryl, said aryl being, besides the substituent R¹⁰, further substituted or not further substituted, and said aryl comprising from 0-5 heteroatoms; with the proviso that if B_(X) is a C4 aryl, it comprises at least one heteroatom in the aromatic ring so as to provide said aryl, wherein any B_(X) may also be independently selected from substituted or unsubstituted vinylene (

) and ethynylene (

); wherein R¹⁰ is independently selected from H, halogen, and a C1-C20 hydrocarbon comprising from 1-20 heteroatoms.

According to a preferred embodiment, R¹⁰ is independently as defined substituents R₅₁-R₁₄₃.

According to an embodiment, any B_(X) is independently selected from the moieties of formula (2)-(29) and (25-37) above, as further defined above. According to an embodiment, B_(X) is independently as A_(Z) defined above.

According to an embodiment, R¹-R⁸ and R¹⁰ are defined as R₅₁-R₁₄₃ above.

According to an embodiment, the substituents R¹-R⁸ are selected, independently one from the other, from H, halogen, and from substituents comprising π-system conjugated to the π-system of the bipyridine ligand of formula (XV). Preferably, the substituents R¹-R⁸ are selected, independently one from the other, from H, and from a substituted or unsubstituted C2-C20 alkenyl and from a substituted or unsubstituted aryl, and may comprise 0-10 heteroatoms. For example, the alkenyl may be substituted by an aryl and vice versa. The aryl and or alkenyl may both be substituted by alkoxyl and/or by a polyether, for example.

According to an embodiment, ligand L₂ corresponds to the pyridine ligands (a), (b), (c), (d), (g), (h), (i), or (j) as defined and disclosed in WO 2006/010290A1 (page 6-8). Preferably, the bipyridine ligand of formula (XV) is a ligand of formula (a) or (a′) of WO 2006/010290 (for (a′), see page 8).

The compounds of the invention are useful as ligands in organometallic compounds, in particular in dyes. The invention thus also encompasses organometallic compounds, in particular dyes comprising the compounds of the invention. The dyes of the invention have advantageous properties when used as sensitizing dyes in optoelectronic and/or electrochemical devices. In particular, the dyes of the invention have advantageous properties when used as sensitizing dyes in photoelectric conversion devices, such as photovoltaic cells and/or solar cells, these terms considered to be equivalents. Preferably, the dyes of the invention are used as sensitizing dyes of dye-sensitized solar cells (DSCs).

The present invention further concerns a photoelectric conversion device comprising a compound of formula (I) or (II) and/or of the embodiments of this compound described above, and/or of a organometallic compound comprising the compound as a ligand. Preferably, the photoelectric conversion device comprises a sensitising dye as defined herein above, in particular a dye selected from the dyes of formula (XI) to (XIII).

Preferably, the photoelectric conversion device is a regenerative cell, preferably a regenerative DSC.

FIGS. 21 and 22 show an embodiment of the dye-sensitized solar cell of the present invention.

According to an embodiment of the present invention, the photoelectric conversion device comprises a light absorption layer 3, which comprises a semiconductor material 4 and, absorbed thereto, a dye layer 5 comprising a dye according to the invention and/or a dye 5 comprising a compound according to the present invention.

According to an embodiment, the DSC of the present invention comprises one or two transparent substrate layers 1, a conductive layer 2, a light absorption layer 3, a charge transport layer 6 and counter electrode 7. Said conductive layer 2, said light absorption layer 3, said electrolyte layer 6 and said counter electrode 7 are preferably connected in this order, for example between two transparent substrate layers 1. The said semiconductor nanoparticle layer 4 is preferably electrically connected with the said conductive layer 2 and the said dyes layer 5 is in electrical contact with the said charge transport layer 6.

According to an embodiment, the photoelectrode comprises one or two semiconductor material films or layers, for example one or two mesoscopic, porous films layers. An example for a preferred semiconductor material is TiO₂. For example, the device comprises a photoelectrode comprising and/or consisting of a single mesoscopic, porous semiconductor material layer. The single layer may have a thickness of ≦10 μm, preferably ≦8 μm, more preferably ≦6 μm and most preferably ≦5 μm.

Preferably, the semiconductor material 4 provides at least part of a photoelectrode. The photoelectrode preferably comprises a nanocrystalline, porous layer of a semiconductor material, said porous layer being characterized by a roughness factor of larger than 20, preferably larger than 200 and even larger than 1000. Preferably, the photoelectrode is a photoanode. The photoelectrode and the counter electrode are preferably provided on support substrates 1, such as transparent glass or plastic, at least one of which is transparent.

Electrode (photo- and counter electrode) materials, and electrolytes that are suitable for the present invention are disclosed in EP1507307, WO2006/010290, WO2007/093961, and in many more. Devices containing electrically conductive charge transporting materials are disclosed in WO2007/107961. In the above references, the manufacturing of such devices is also disclosed. In FIG. 1 of EP1507307, an embodiment of a possible structure of devices of the present invention is disclosed. On page 8, line 10 to page 9, line 51, general information and suitable materials of the preparation of devices encompassed by the present invention is disclosed. Of course, the present invention is not limited to devices as disclosed in these references.

The invention is illustrated by the Examples below, which are not intended to limit the scope of the invention.

EXAMPLES Experimental

NMR spectra were recorded on a Bruker AMX 500 (¹H NMR: 500 MHz, ¹³C NMR: 125 MHz) or an Avance 400 spectrometer (¹H NMR: 400 MHz, ¹³C NMR: 100 MHz), at 25° C. Chemical shift values (8) are expressed in parts per million using residual solvent protons (DMSO-d₆: ¹H δ=2.5 ppm and ¹³C δ=39.4 ppm) as internal standard. Melting points were determined using a BüchiB-545 apparatus. Elemental analyses were performed on an Elementar Vario EL (University of Ulm). ESI and EI mass spectra were recorded on a micromass ZMD or a VarianSaturn 2000 GC-MS, MALDI-TOF on a Bruker Daltonics Reflex III. Optical measurements were carried out in 1 cm cuvettes with Merck Uvasol grade solvents, absorption spectra recorded on a Perkin Elmer Lambda 19 spectrometer and fluorescence spectra on a Perkin Elmer LS 55 spectrometer. Cyclic voltammetry experiments were performed with a computer-controlled EG&G PAR 273 potentiostat in a three-electrode single-compartment cell with a platinum working electrode, a platinum wire counter electrode, and an Ag/AgCl reference electrode. All potentials were internally referenced to the ferrocene/ferrocenium couple.

Example 1 4,4′-Di(thiophen-2-yl)-2,2′-bipyridine (1)

To a mixture of 4,4′-Dibromo-2,2′-bipyridine (2 g, 6.36 mmol), tributylstannyl thiophene (5.7 g, 15.28 mmol) in 10 mL dry degased toluene:THF (2:1) in a schlenk tube was added Pd(PPh)₃Cl₂ (134 mg, 191 μmol) and CsF (4.84 g, 31.8 mmol). The reaction mixture was heated at 110° C. for 8 h. The completion of the reaction was checked by TLC. The solvent was removed under reduced pressure and the crude product was purified by column chromatography (basic Al₂O₃) eluting with a mixture of 1:1 (v/v) ratio hexane:DCM. After evaporation of the solvent 1 (1.93 mg, 6.03 mmol, 95%) was obtained as a colorless solid. M.p.>250° C.; ¹H NMR: (d₆-DMSO, 400 MHz) δ ppm: δ ppm 7.25 (t, 1H), 7.78 (d, J=4.97 Hz, 2H), 7.89 (d, J=3.32 Hz, 1H), 8.59 (s, 1H), 8.72 (d, J=5.13 Hz, 1H). ¹³C NMR: (d₆-DMSO, 100 MHz) δ ppm: 115.89, 119.85, 126.64, 128.43, 128.95, 140.25, 141.66, 150.10, 155.59. Elemental analysis: calc. for C₁₈H₁₂N₂S₂ C, 67.47; H, 3.77; N, 8.74%; found: C, 67.52; H, 3.81%; N, 8.71%.

Example 2 5,5′-(2,2′-bipyridine-4,4′-diyl)dithiophene-2-carboxylic acid (2)

To a solution of n-BuLi (4.29 mL, 6.87 mmol, 1.6 M in n-hexane) in 60 mL dry THF at −78° C. was added diisopropylamine (759 μL, 7.5 mmol) dropwise. The reaction mixture was stirred for 30 min and then allowed to warm to room temperatre for 10 min and recooled to −78° C. 1 (1 g, 3.12 mmol.) in 100 mL THF was added slowly and the reaction mixture was stirred for 30 min. Dry ice was taken in another flask and then CO₂ was bubbbled to the reaction flask via a cannula. White solid was precipitated. To this 1M HCl was added slowly to make the pH to ˜5. The solid was filtered and washed with water and methanol. Recrystallized from hot DMSO to obtain the desired product 2 (FIG. 1) as white solid (892 mg, 2.2 mmol, 78%). M.p.>300° C.; ¹H NMR: (d₆-DMSO, 400 MHz) δ ppm: 7.81 (d, J=3.89 Hz, 1H), 7.88 (dd, J=5.02, 1.69 Hz, 1H), 7.96 (d, J=3.93 Hz, 1H), 8.66 (d, J=1.43 Hz, 1H), 8.81 (d, J=5.20 Hz, 1H); ¹³C NMR: (d₆-DMSO, 100 MHz) δ ppm: 116.22, 119.88, 126.44, 133.45, 140.56, 145.68, 149.79, 155.47, 161.63, 169.08. Elemental analysis for C₂₀H₁₂N₂O₄S₂: calcd. C, 58.81; H, 2.96; N, 6.86%, found: C, 58.91; H, 2.93; N, 6.81%.

Example 3 Ru(5,5′-(2,2′-bipyridine-4,4′-diyl)dithiophene-2-carboxylic acid) (4,4′-dinonyl-2,2′-bipyridine)(NCS)₂ (3)

RuCl₂(p-cymene)₂ (112.4 mg, 0.184 mmol) and dnbpy (150 mg, 0.367 mmol) were taken in a Schlenk tube and dissolved in dry DMF (30 mL). The reaction mixture was heated to 60° C. under argon for 4 h with constant stirring. Subsequently, dtcbpy (150 mg, 0.367 mmol) was added to this reaction flask and the reaction mixture was refluxed under dark at 140° C. for 4 h. Finally, an excess of NH₄NCS (837 mg, 11.0 mmol) was added to the reaction mixture and the reflux continued for another 4 h. The reaction mixture was cooled to room temperature, and the solvent was removed by using a rotary evaporator under vacuum. Water was added to the flask, and the insoluble solid was collected on a sintered glass crucible by suction filtration. The solid was washed with distilled water and diethyl ether and then dried under vacuum. The crude complex was dissolved in methanolic sodium hydroxide solution and purified on a Sephadex LH-20 column with methanol as eluent. The collected main band was concentrated and divided into two halves and one part titrated quickly to pH 3.2 to isolate compound 3a. The second half then slowly titrated with an acidic methanol solution (HNO₃) to pH 4.8 to isolate compound 3 b. The precipitated 3 a was collected on a sintered glass crucible by suction filtration and dried. ¹H NMR (d₄-MeOH, 400 MHz) δ ppm: 0.8 (t, 3H), 0.85 (t, 3H), 1.1-1.5 (m, 24H), 1.57 (m, 2H), 1.82 (m, 2H), 2.65 (t, 2H), 2.91 (t, 2H), 7.12 (dd, J=5.76, 0.93 Hz, 1H), 7.48 (d, J=5.73 Hz, 1H), 7.54 (d, J=2.20 Hz, 1H), 7.76 (d, J=3.55 Hz, 1H), 7.83 (dd, J=5.61, 0.96 Hz, 1H), 7.88 (d, J=3.53 Hz, 1H), 8.03 (d, J=3.84 Hz, 1H), 8.24 (d, J=3.90 Hz, 1H), 8.27 (dd, J=5.91, 1.71 Hz, 1H), 8.54 (s, 1H), 8.69 (s, 1H), 9.03 (s, 1H), 9.09 (d, J=5.76 Hz, 1H), 9.16 (s, 1H), 9.26 (d, J=5.91 Hz, 1H).

Example 4 Ru(bis[5,5′-(2,2′-bipyridine-4,4′-diyl)dithiophene-2-carboxylic acid)] (NCS)₂ (4)

RuCl₂(p-cymene)₂ (74 mg, 0.122 mmol) and dtbpy (200 mg, 0.489 mmol) were taken in a Schlenk tube purged with argon and dissolved in dry DMF (30 mL). The reaction mixture was heated in dark to 145° C. for 5 h with constant stirring. Subsequently, an excess of NH₄NCS (1.1 g, 14.6 mmol) was added to the reaction mixture and the reflux continued for another 4 h. The reaction mixture was cooled to room temperature, and the solvent was removed by using a rotary evaporator under vacuum. Small amount of water was added to the dried solid and filtered on a sintered glass crucible by suction filtration. The solid was further washed with distilled water and diethyl ether and then dried under vacuum. The crude complex was dissolved in methanolic tetrabutylammonium hydroxide solution and purified on a Sephadex LH-20 column with methanol as eluent. The collected main band was concentrated and then slowly titrated with an acidic methanol solution (HNO₃) to pH 4.4. The precipitate (compound 4 in FIG. 3) was collected as 2TBA salt on a sintered glass crucible by suction filtration and dried under vacuum. ¹H NMR (d₄-MeOH/d₆-DMSO, 400 MHz) δ ppm: 0.9 (t, 12H), 1.29 (m, 8H), 1.52 (m, 8H), 3.2 (t, 8H), 7.38 (dd, J=6.11, 1.88 Hz, 1H), 7.57 (d, J=3.76 Hz, 1H), 7.61 (d, J=6.13 Hz, 1H), 7.70 (d, J=3.63 Hz, 1H), 7.84 (d, J=3.94 Hz, 1H), 8.05 (d, J=3.87 Hz, 1H), 8.08 (dd, J=5.97, 1.77 Hz, 1H), 8.99 (s, 1H), 9.14 (s, 1H), 9.31 (d, J=5.96 Hz, 1H). Elemental Analysis for C₇₄H₉₄N₈O₈RuS₆.1[(C₄H₉)₄N].5H₂O calcd. C, 50.97; H, 5.16; N, 7.17%, found. C, 51.12; H, 4.44; N, 7.15%.

Example 5 General Device Fabrication

The cells consisted of a mesoscopic TiO₂ film composed of a 7 μm thick transparent layer of 20 nm sized TiO₂ anatasenanoparticles onto which a second 5 μm thick scattering layer of 400 nm sized TiO₂ was superimposed. The double layer films were heated to 520° C. and sintered for 30 min, then cooled to 80° C. The electrode was immersed for 16 hours into the dye solution (150 μM) containing 10% DMSO in a acetonitrile/tert-butyl alcohol-mixture (volume ratio:1:1). The devices were fabricated with the low-volatile electrolyte coded Z946. The Z946 electrolyte contains 3-methoxypropionitrile as a solvent and 1.0 M 1,3-dimethylimidazolium iodide (DMII), 0.15 M 1₂, 0.5 M n-butylbenzimidazole as well as 0.1 guanidiniumthiocyanate (GuNCS) as solutes. The cell was sealed with a 25 μm-thick transparent Surlyn ring (from DuPont) at 130° C. for 15 seconds to the counter electrode (FTO glass, 15 Ωcm⁻², coated with a platinum solution chemically deposited at 450° C. for 15 min). The cells were filled with the electrolyte through a pre-drilled hole in the counter electrode. The hole was then sealed with a Bynel disc and a thin glass to avoid leakage of the electrolyte.

Examples 6-14 Results obtained with dye 3 of Example 3 Device Fabrication:

Dye sensitized solar cells (DSCs) with double or single thin layers of TiO₂ particles were prepared and coated with different dyes with or without co-adsorbed compounds.

5.5 and 3.3 μm thick transparent layers of 20 nm TiO₂ particles were screen printed on a fluorine-doped SnO₂ (FTO) conducting glass electrode.

Double layered films of TiO₂ particles (7+5 μm) were prepared by first screen printing a 7 μm of 20 nm TiO₂ particles on the fluorine-doped SnO₂ (FTO) conducting glass electrode, followed by coating with a 5 μm thick second layer of 400 nm light scattering anatase particles.

The details for the preparation of the TiO₂ films have been described by Wang, P.; Zakeeruddin, S. M.; Comte, P.; Charvet, R.; Humphry-Baker, R.; Gratzel, M. J. Phys. Chem. B 2003, 107, 14336.

The TiO₂ films are first sintered at 500° C. for 30 min and then cooled to about 80° C. in air. Then, the TiO₂ film electrodes are dipped into dye solutions (150 μM) with and without the coadsorbent in a mixture of 10% DMSO and acetonitrile and tert-butyl alcohol (volume ratio, 1:1) at room temperature for 16 h to adsorb the dye. Thereafter, the films were washed with acetonitrile and dried by air flow.

The cells were sealed to the counter electrode and supplied with the low-volatile Z946 electrolyte solution as described in Example 5 above.

The photoelectric characterization of the various dye-sensitized solar cells is detailed in Table 3 below and is further illustrated in FIGS. 7-16.

TABLE 1 Structure and photoelectric characteristics of DSCs of the invention and of the prior art. IPCE V_(OC) Eff. max λmax Ex. TiO₂ film Dye Co-adsorbant (V) J_(SC) ¹ FF (%) (%) (nm) 6 double 3a — 0.678 13.7 0.71 6.6 58.8 530 7 (7 + 5 μm) 3b — 0.709 14.8 0.72 7.6 60.1 550 8 double 3b — 0.709 14.8 0.72 7.6 60.1 550 9 (8.5 + 5 3b DINHOP² (4:1) 0.732 14.9 0.72 8.0 63.8 550 10 μm) 3b GBA³ (1:1) 0.778 12.9 0.74 7.5 65.1 550 11 single thin Z907⁴ GBA³ (1:1) 0.800 11.1 0.74 6.6 73.8 520 12 (5 μm) 3b GBA³ (1:1) 0.744 12.7 0.73 7.0 62.5 520 13 single thin Z907⁴ GBA³ (1:1) 0.810  8.9 0.74 5.4 70.7 520 14 (3 μm) 3b GBA³ (1:1) 0.753 10.5 0.71 5.7 66.6 540 ¹(mA/cm²); ²DINHOP = bis-(3,3-dimethyl-butyl)-phosphinic acid; ³GBA = 4-guanidino butyric acid was obtained from Fluka; ⁴state of the art dye [cis-RuLL′(SCN)₂] (L = 4,4′-dicarboxylic acid-2,2′-bipyridine, L′ = 4,4′-dinony1-2,2′-bipyridine).

Synthesis of DINHOP (bis-(3,3-dimethyl-butyl)-phosphinic acid)

To 3,3-dimethylbutene (4.00 g, 47.5 mmol) hypophosphrous acid (aq. 50%) (0.80 g, 11.9 mmol) and di-tert.-butylperoxide (neat, 0.30 g, 2.4 mmol) was added in a Buchi reactor (10 ml), heated to 135° C. and stirred for 22 hours. The reaction mixture was filtered, and the solid was washed thoroughly with water twice, and with a little acetone. Recrystallization from n-hexane yielded 1.01 g (73%) bis-(3,3-dimethyl-butyl)-phosphinic acid. ¹H NMR (CDCl₃) d ppm: 0.92 (18H, s), 1.49 (4H, m), 1.64 (4H, m), 9.15 (1H, br)

31P NMR (CDCl₃) d ppm: 62.8 (s),

HR-MS m/z 235.1821 (C12H₂₇O₂P).

Conclusion for Examples 8-14

As can be seen in particular from comparing Examples 11-14 in Table 1 (FIGS. 13-16), the dye 3 b of the present invention surprisingly results in devices with higher conversion efficiencies (Eff. (%)) than the state of the art dye Z907 ([cis-RuLL′(SCN)₂ (L=4,4′-dicarboxylic acid-2,2′-bipyridine, L′=4,4′-dinonyl-2,2′-bipyridine)], if the dye is provided on a thin TiO₂ film of 3 or 5 μm.

Such high conversion efficiencies (7%, Example 12; 5.7% Example 14 in Table 1) are very surprising for a Ru-dye on such thin TiO₂ films (5 and 3 μm, respectively). In particular, in the cells of Examples 12 and 14, the J_(SC) values are 14.4% and 18%, respectively, higher than in the cells of the comparative Examples 11 and 13 using dyes of the prior art.

These results show that dyes of the present invention has superior performance over the prior art dyes with thin TiO₂ films due to red shift in the absorption spectra and increase in the molar extinction coefficient. This approach allows designing efficient panchromatic sensitizers with increased photovoltaic conversion efficiencies with ultra thin titania films.

Examples 15-17 Device Stability Tests

The devices obtained in Examples 8-10 were subjected to the visible light-soaking (1 sun; 100 mW/cm²) at 60° C. for 1000 h.

The results can be seen in FIG. 12 and Table 2 below. It can be seen that the devices with the compound 3 b dye exhibit excellent stability.

TABLE 2 DSCs of Examples 8-10 (Table 1), following exposure to full sunlight for 1000 hours V_(OC) J_(SC) Eff. Stability Example Dye Co-adsorbent EL State (V) (mA/cm²) FF (%) (%) 15 3b — Z946 Final 0.648 14.2 0.74 6.8  90 16 3b DINHOP (4:1) Z946 Final 0.660 16.0 0.73 7.7  98 17 3b GBA (1:1) Z946 Final 0.710 15.0 0.74 7.9 106

Examples 18-21 Dye Sensitized Solid State Solar Cells with Dyes of the Invention on 2 μm Mesoporous TiO₂ Film Device Fabrication:

For solid-state device fabrication, a spray pyrolysis technique was used to coat the FTO conducting glass substrates (LOF Industries, TEC 15Ω/square, 2.2 mm thickness) with a thin compact layer of TiO₂ in order to prevent electron-hole recombination arising from direct contact between the hole-conductor (spiro-OMeTAD) and the highly doped FTO layer. A 1.8 μm mesoporous layer of the TiO₂ nanoparticles with a typical diameter of 20 nm was deposited by doctor-blading on top of this compact layer. The TiO₂ electrodes were stained by dipping in a dye solution for 5 h of 0.3 mM dye and 10 mM cheno in dichloromethane. The spiro-OMeTAD solution (137 mM in chlorobenzene) contained final concentrations of 112 mM tert-butylpyridine and 21 mM Li—[CF₃SO₂]₂N (added from highly concentrated acetonitrile solutions). Finally, a gold contact (100 nm) was deposited on the organic semiconductor film by evaporation (EDWARDS AUTO 500 Magnetron Sputtering System).

Results and Conclusion:

As shown in Table 3 the dye 3 b with spiro-MeOTAD as hole transport material gave superior photovoltaic performance compared to prior art dye Z907 under similar conditions using ultra thin mesoporous TiO₂ films.

TABLE 3 Solid-state device results with Acedic-TiO₂, 2 μm film, overnight dipping Exam- Efficien- ple Condition Substrate J_(SC) V_(OC) FF cy(%) 18 3b Acidic-TiO₂ 6.98 708.72 48.5 2.4 19 3b + GBA 9.15 776.32 45.6 3.2 20 3b + GBA 50 nm 7.52 796 60 3.6 21 Z907 + GBA 50 nm 6 824.3 63.5 3.1

Example 22 Results of Compound 4 of Example 4

The electronic absorption spectrum of compound 4 in DMF is displayed in FIG. 17 and the data are summarized in Table 4 below. Compound 4 showed broad absorption bands in the 300 to 750 nm region. The two high-energy bands at 287 and 331 nm are due to intra-ligand π-π* transitions. The absorption spectrum of compound 4 is dominated by metal to ligand charge transfer transitions (MLCT). The lowest energy MLCT band at 563 nm is 28 nm red-shifted compared to the standard N719 sensitizer (see below) because of the extention of 7C-conjugation in the anchoring ligand and increased HOMO energy level.

The N719 dye described previously is the bis-tetrabutylammonium (TBA) salt of cis-di(thiocyanato)-bis[2,2′-bipyridyl-4,4′-dicarboxylic acid] ruthenium(II), see (a) M. K. Nazeeruddin, A. Kay, L. Rodicio, R. Humpbry-Baker, E. Miiller, P. Liska, N. Vlachopoulos, M. Grätzel, J. Am. Chem. Soc. 1993, 115, 6382. (b) Md. K. Nazeeruddin, F. De Angelis, S. Fantacci, A. Selloni, G. Viscardi, P. Liska and M. Gratzel, J. Am. Chem. Soc. 2005, 127, 16835.

TABLE 4 Spectroscopic and electrochemical data of compound 4 and N719 measured in DMF. (HOMO/LUMO vs. Fc/Fc⁺ _(vac) = −5.1 eV) λ_(abs) (nm) λ_(em) E⁰ _(ox) E⁰ _(red1) E⁰ _(red2) HOMO LUMO ΔE Dye (ε [L mol⁻¹ cm⁻¹]) (nm) (V) (V) (V) (eV) (eV) (eV) 4 287 (59000) 800 0.28 −1.86 −2.08 −5.33 −3.37 1.96 331 (62300) 426 (24800) 563 (23200) N719 312 (47200) 800 0.39 −2.17 — −5.38 −3.06 2.32 388 (13800) 535 (13500)

TABLE 5 Comparison of photovoltaic parameters under full sunlight intensity of compound 4 and N719 adsorbed on nanocrystalline TiO₂ films of various thicknesses. TiO₂ Film J_(sc) Thickness (mA Dye (μm) V_(oc) (V) cm⁻²) FF η (%) 4 3.3 0.68 12.2 0.74 6.1 5.5 0.67 14.1 0.73 6.9 7 + 5 0.66 15.8 0.73 7.6 N719 3.3 0.74 9.1 0.71 4.8 5.5 0.72 12.5 0.70 6.3 7 + 5 0.71 15.3 0.71 7.7

Importantly, an increase of 72% of the molar extinction coefficient was observed for the longest wavelength MLCT band as a consequence of the insertion of thiophene units to the ligand compared to N719 sensitizer. The emission data of compound 4 were obtained in an air-equilibrated DMF solution at 298K by exciting at the low energy MLCT absorption band, showing a week emission maximum at 800 nm.

HOMO and LUMO energy levels of compound 4 were determined by cyclic voltammetry (Table 4). The complex showed an oxidation wave at 0.28 V (vs. Fc VFc), which is assigned to the oxidation of the Ru^(II) center. Compared to standard N719 dye, the metal centre oxidation is cathodically shifted by 110 mV indicating the electron-rich character of the new ligand as a result of the thiophene insertion. Two reversible reduction waves at −1.86 and −2.08 V (vs. Fc⁺/Fc) can be assigned to successive one electron reductions of the bipyridine ligands. The first cathodic potential of compound 4 is by 310 mV more positive than that of N719.

The excited state oxidation potential of a sensitizer plays an important role in electron transfer processes. The quasi-Fermi level of the TiO₂ photoanode and the redox level of the I₃ ⁻I⁻-based electrolyte are situated at around −4.0 eV and −4.83 eV vs. vacuum, respectively. The HOMO level of compound 4 is located at −5.33 eV, the LUMO level at −3.37 eV. Overall, the HOMO-LUMO band gap of compound 4 (E_(g)=1.96 eV) is approximately 360 meV smaller compared to N719 (E_(g)=2.32 eV), which is also reflected in the red-shift of the absorption spectrum. The position of the LUMO level of compound 4 is sufficiently more negative than the TiO₂ conduction band to facilitate efficient electron transfer from the excited dye to TiO₂. On the other hand, the HOMO level of compound 4 is sufficiently below the energy level of the redox mediator allowing dye regeneration.

Absorption spectra of compound 4 and N719 adsorbed on a 3.3 μm transparent TiO₂ thin film showed features similar to those of corresponding spectra in solution, but exhibited a slight red-shift due to interaction of the anchoring groups and the TiO₂ surface (FIG. 18). These transparent thin films were used to investigate differences in photovoltaic performance of N719 and compound 4 dyes.

The monochromatic incident photon-to-current conversion efficiency (IPCE) is defined as the number of electrons generated by light in the external circuit divided by the number of incident photons as a function of excitation wavelength. FIG. 19 shows the IPCE spectra obtained with DSSC devices of compound 4 and N719 dye with 3.3 μm transparent photoanodes and a 3-methoxypropionitrile (MPN) containing low volatile electrolyte. N719 and compound 4 exhibited at 550 nm IPCE values of 67 and 74%, respectively, with an extended red response for compound 4. Under standard global AM 1.5 solar conditions, compound 4 sensitized cells gave a short-circuit photocurrent density (J_(sc)) of 12.2 mA cm⁻², an open-circuit voltage (V_(oc)) of 0.68 V, and a fill factor (FF) of 0.74, corresponding to an overall conversion efficiency of 6.1% (FIG. 20). Such a high performance is very intriguing for a Ru^(II)-dye on a 3.3 μm thin TiO₂ film in combination with a low volatile electrolyte. Under similar conditions N719 dye-sensitized cells gave an overall conversion efficiency of only 4.8%. The photovoltaic parameters are given in Table 5. The J_(sc) value of the compound 4 sensitizer is 34% higher compared to N719. This observation is in accordance with the red-shifted absorption in the visible region and the increased molar extinction coefficient.

The influence of nanocrystalline TiO₂ film thickness on the photovoltaic performance with compound 4 sensitizer was studied using film thicknesses of 3.3 and 5.5 μm. Additionally, a thick TiO₂ film composed of 7 μm transparent layer and 5 μm scattering layer was tested. The detailed photovoltaic parameters of corresponding devices with compound 4 and N719 are given in Table 5. Increasing the film thickness from 3.3 over 5.5 to 7+5 μm for compound 4 resulted in an increase of the current densities from 12.2 over 14.1 to 15.8 mA cm⁻². As a consequence, the overall cell performance was increased from 6.1 to 7.6% under full sunlight. It is interesting to note that with thinner films the photovoltaic performance of compound 4 devices outperformed N719 devices, whereas, with double layer films the performance was nearly identical.

In conclusion, we have designed and synthesized a new anchoring ligand, 5,5′-(2,2′-bipyridine-4,4′-diyl)-bis(thiophene-2-carboxylic acid) and its ruthenium complex compound 4 Extending the π-conjugation of the anchoring ligand increased the device performance in thin films as a result of the increased molar extinction coefficient and enhanced spectral response in the red wavelength region. This class of sensitizers containing thiophene in the anchoring site has not been previously reported. This approach allows designing efficient panchromatic sensitizers with increased photovoltaic conversion efficiencies. 

1-19. (canceled)
 20. A compound of formula (III) and/or (IV) below, respectively:

wherein, A₁ and A₂ are defined as a substituent of formula (1) below:

wherein n is an integer of 1-2, and Z is an integer of the group of integers 1, . . . , n, wherein any A_(Z) represents the Z^(th) moiety of the n successive moieties A, wherein any A_(Z) may be different from any other A_(Z); wherein any A_(Z) is independently selected from a C4-C20 aryl, said aryl being, besides the substituent Anc, further substituted or not further substituted, and said aryl comprising from 1-10 heteroatoms; wherein, if n=2, A_(Z) may also be selected from vinylene (

) and ethynylene (

), wherein said vinylene may be substituted; with the proviso that at least one A_(Z) is an aryl as defined above; wherein, if n≧1, the first moiety A₁ (A_(Z=1)) is selected from the moieties of formula (2)-(24) as defined below:

wherein A and B, if applicable, are each selected independently from S (sulfur), O (oxygen), and Se (selenium); X is selected from any one of C, Si, Ge, Sn or Pb; preferably from C and Si, most preferably it is C; substituents R₅₁-R₁₃₁, if applicable, are independently one from the others selected from H, halogen and a C1-C20 hydrocarbon comprising from 0 to 20 heteroatoms; wherein A₂ may be present (n=2) or may be absent (n=1), wherein, if A₂ is absent, the anchoring group Anc is directly connected to A₁; wherein Anc is an independently selected anchoring group; wherein any one of R₂₀-R₃₄ is, independently from the others, selected from H, halogen or a C1-C20 hydrocarbon comprising from 0 to 20 heteroatoms or a substituent of formula (1); wherein, if more than one of R₂₀-R₃₄ are a substituent of formula (1), any n of such substituent may be the same or different from the n of another such substituent of formula (1), and any A_(Z) may be different from the respective A_(Z) of another such substituent of formula (1).
 21. The compound of claim 20, wherein said compound of formula (III) and/or (IV) is selected from a compound of formula (V) or (VI) below:

wherein A₁ and A₂ are defined as A_(Z) above; wherein, if n=2, Az may also be selected from vinylene (

) and ethynylene (

), wherein said vinylene may be substituted; with the proviso that at least one A_(Z) is an aryl as defined above; wherein, if n≧1, the first moiety A₁ (A_(Z=1)) is selected from the moieties of formula (2)-(24) as defined above; wherein A₂ may be present (n=2) or may be absent (n=1), wherein, if A₂ is absent, the anchoring group Anc is directly connected to A₁; wherein Anc is defined as above; wherein R₁, R₂, R₄, R₅, R₇, R₁₀, R₁₂, R₁₃, R₁₅, R₁₆, R₁₈ and R₁₉ are defined as R₂₀-R₃₄ above.
 22. The compound of claim 20, wherein any moiety A_(Z), A₁ and A₂, as applicable, may be independently selected from the moieties (2)-(24) above and from the moieties (25)-29) below, with the proviso that at least one moiety is selected from any one of moieties (2)-(24) above:

wherein A and B, if applicable, are each selected independently from S (sulfur), 0 (oxygen), and Se (selenium); X is selected from any one of C, Si, Ge, Sn or Pb; preferably from C and Si, most preferably it is C; substituents R₁₃₂-R₁₄₃, if applicable, are independently one from the others selected from H, halogen and a C1-C20 hydrocarbon comprising from 0 to 20 heteroatoms.
 23. The compound of claim 20, wherein, if in a substituent of formula (1) n>1, the first moiety A₁ (A_(Z=1)) is selected from the moieties of formula (2)-(5).
 24. The compound of claim 20, wherein the anchoring group (Anc) is selected from —COOH, —PO₃H₂, —PO₄H₂, —P(R₁₀₀)O₂H, —SO₃H₂, —CONHOH⁻, acetylacetonate, deprotonated forms of the aforementioned, salts of said deprotonated forms, and chelating groups with π-conducting character; wherein R₁₀₀ is a hydrocarbon comprising from 1 to 20 carbons and 0-20 heteroatoms, said hydrocarbon being covalently bound to the P atom of said phosphinic acid group by a carbon atom; and wherein R₁₀₀ may be further covalently connected to the bi- or polypyridine ligand carrying the anchoring group Anc.
 25. The compound of claim 20, wherein A₁ is the moiety of formula (2) or (4).
 26. The compound of claim 20, R₂₀-R₃₄ of formula (III) and (IV) are independently selected from H, halogen or C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, and from C4-C15 aryl, said alkyl, alkenyl, and alkynyl being linear or branched and said alkyl, alkenyl, and alkynyl optionally being further substituted, and wherein said aryl, if is a C4 aryl, comprises at least one heteroatom selected from O, S and N in the ring so as to provide an aromatic ring.
 27. The compound of claim 21, wherein R₁, R₂, R₄, R₅, RrRio, R₁₂, R₁₃, R₁₅, R₁₆, R₁₈ and R₁₉ formula (V) and/or (VI) are independently selected from H, halogen or C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, and from C4-C15 aryl, said alkyl, alkenyl, and alkynyl being linear or branched and said alkyl, alkenyl, and alkynyl optionally being further substituted, and wherein said aryl, if is a C4 aryl, comprises at least one heteroatom selected from O, S and N in the ring so as to provide an aromatic ring.
 28. The compound of claim 20, wherein n is 1 and wherein in every substituent of formula (1), A₁ (A_(Z=1)) is selected from any one of any of moieties of (25)-(32) below:


29. The compound of claim 28, wherein the substituents R₅₁-R₁₄₃, in as far as present, are independently selected from H, halogen, anchoring groups as defined herein, cyano, C1-C10 alkyl and C2-C10 alkenyl, said alkyl and alkenyl being linear or branched and optionally further substituted.
 30. The use of the compounds of formula (III) and/or (IV) as defined in claim 20 as an anchoring ligand in an organometallic sensitizer of a dye sensitized solar cell.
 31. A dye of formula (XI), (XII) or (XIII): M L₁ L₂ L₃ L₄  (XI) M L₅ L₃ L₄ L₆  (XII) M L₅ L₂ L₄  (XIII) wherein M is a metal atom selected from Ru, Os, Ir, Re, Rh, and Fe; wherein L₁ is a bipyridine ligand of formula (III) according to claim 20; wherein L₂ is, independently from L_(I), a ligand of formula (III) of claim 20 or a bidentate ligand being a C3-C30 hydrocarbon comprising from 2 to 20 heteroatoms; wherein L₃, L₄ and L₆ are monovalent ligands independently selected from H₂O, —Cl, —Br, —I, —CN, —NCO, —NCS and —NCSe; L₅ is a ligand of formula (IV) according to claim
 20. 32. A dye of formula (XI), (XII) or (XIII): M L₁ L₂ L₃ L₄  (XI) M L₅ L₃ L₄ L₆  (XII) M L₅ L₂ L₄  (XIII) wherein M is a metal atom selected from Ru, Os, Ir, Re, Rh, and Fe; wherein L₁ is a bipyridine ligand of formula (V) according to claim 21; wherein L₂ is, independently from L₁, a ligand of formula (V) of claim 21 or a bidentate ligand being a C3-C30 hydrocarbon comprising from 2 to 20 heteroatoms; wherein L₃, L₄ and L₆ are monovalent ligands independently selected from H₂O, —Cl, —Br, —I, —CN, —NCO, —NCS and —NCSe; L₅ is a ligand of formula (VI) according to claim
 21. 33. The dye of claim 31, wherein L₂ is a bipyridine ligand of formula (XV)

wherein the substituents R¹-R⁸ are selected, independently one from the other, from H, halogen, and C1-C20 hydrocarbons comprising from 0 to 20 heteroatoms.
 34. The dye of claim 33, wherein one or more of R¹-R⁸ are selected, independently one from the other, from substituents of formula (51) below:

wherein m is an integer of 1-10, and X is an integer of the group of integers 1, . . . , m, wherein any B_(X) represents the X^(th) moiety of the m successive moieties B, wherein any B_(X) may be different from any other B_(X); wherein, if more than one of R¹-R⁸ of the compound of formula (XV) are a substituent of formula (51), any m of such substituent may be the same or different from another such substituent of formula (51), and any B_(X) may be different from the respective B_(X) of another such substituent of formula (51); wherein any B_(X) is independently selected from a C4-C20 aryl, said aryl being, besides the substituent R¹⁰, further substituted or not further substituted, and said aryl comprising from 0-5 heteroatoms; wherein any B_(X) may also be independently selected from substituted or unsubstituted-vinylene (

) and from ethynylene (

); wherein R¹⁰ is independently selected from H, halogen, and a C1-C20 hydrocarbon comprising from 0-20 heteroatoms.
 35. The dye of claim 34, wherein any B_(X) is independently selected from the moieties of formula (2)-(29) above.
 36. A photoelectric conversion device comprising a compound of formula (III) and/or (IV) as defined in claim 20 and/or a dye according to claim
 31. 37. The device of claim 36, comprising a light absorption layer (3), which comprises a semiconductor material (4) and, absorbed thereto, a dye layer (5) comprising a dye according to claim 31 and/or a dye (5) comprising a compound according to claim
 20. 